Conventional golf balls can be divided into several general classes: (a) solid golf balls having one or more layers, and (b) wound golf balls. Solid golf balls include one-piece balls, which are easy to construct and relatively inexpensive, but have poor playing characteristics and are thus generally limited for use as range balls. Two-piece balls are constructed with a generally solid core and a cover and are generally popular with recreational golfers because they are very durable and provide maximum distance. Balls having a two-piece construction are commonly formed of a polymeric core encased by a cover. Solid golf balls also include multi-layer golf balls that are comprised of a solid core of one or more layers and/or a cover of one or more layers. These balls are regarded as having an extended range of playing characteristics. These balls are generally easy to manufacture, but are regarded as having limited playing characteristics.
A variety of golf balls designed to provide a wide range of playing characteristics, i.e., the compression, velocity, “feel,” and spin, that can be optimized for various playing ability, are known in the prior art. Typical golf ball construction includes a core formed from polybutadiene that is chemically crosslinked with zinc diacrylate and/or other similar crosslinking agents. In addition, golf ball formulations have included sulfur-based components in an effort to provide improved golf balls, as discussed below.
U.S. Pat. No. 5,776,012 discloses a solid golf ball having a core and a cover. The core is formed from vulcanized molded material of a rubber composition that contains a number of materials, including a base rubber, a metal salt of α,β-unsaturated carboxylic acid, an organic peroxide and an organosulfur compound and/or a metal-containing organosulfur compound that is present from 0.3 to 2.3 parts by weight based on 100 parts by weight of base rubber. The further discloses particular organosulfur compound and metal-containing organosulfur compounds, including diphenyl disulfide, dixylyl disulfide, pentachlorothiophenol (“PCTP”), thiobenzoic acid, morpholine disulfide, as well as zinc salts of thiophenols and thiocarboxylic acids.
U.S. Pat. No. 6,184,301 discloses solid golf balls having a solid core and cover, where the core is formed from a base material that contains several materials, including a base rubber, an unsaturated carboxylic acid or metal salt thereof, and a sulfur halide that is present from 0.03 to 0.5 parts by weight based on 100 parts by weight of the base rubber. Particular sulfur halides include disulfur dichloride, sulfur dichloride, sulfur monochloride, thionyl chloride and sulfur bromide.
U.S. Pat. No. 5,929,171 discloses a solid golf ball having a core and cover formed on the core, where the core is formed from a rubber composition that includes a base rubber, and an organosulfur compound that is present from 0.05 to 5.0 parts by weight based on 100 parts by weight of the rubber. The particular organosulfur compounds are 4-methylphenol, bis(4-methacryloylthiopehnyl)sulfide, 4,4′-dithiodibenzene thiol, 4,4′-dibroimodiphenylsulfide, 2-mercaptothiazoline, or mixtures thereof.
U.S. Pat. No. 6,241,625 discloses a solid golf ball having a core and cover, where the core is formed from vulcanized rubber that includes a base rubber, an α,β-unsaturated carboxylic acid or metal salt thereof, an organic peroxide and a sulfide that is present from 0.2 to 1.0 parts by weight per 100 parts by weight of the base rubber. The particular sulfides include diphenyl monosulfides, diphenyl disulfides, diphenyl polysulfides, and morpholine disulfide.
U.S. Pat. No. 6,121,357 discloses a solid golf ball having a core and cover formed on the core, where the core is obtained by vulcanizing a rubber composition comprising a base rubber, a co-crosslinking agent, a vulcanization initiator (such as an organic peroxide), and a filler. The co-crosslinking agent can be a monovalent or divalent metal salt of an α,β-unsaturated carboxylic acid and the filler can include an organic sulfide, such as diphenyl polysulfide, dibenzylpolysulfide, dibenzoyl polysulfide, dibenzothiazoyl polysulfide, 4-methyl phenol sulfide and 4-ethyl phenol sulfide, which can be present from 0.05 to 5.0 parts by weight based on 100 parts by weight of the base rubber.
U.S. Pat. No. 5,919,101 discloses a solid golf ball having a core and cover formed on the core, where the core is formed from a rubber composition having 0.05 to 5 parts by weight of an organic sulfide compound, based on 100 parts by weight of a base rubber. The organic sulfides include polysulfides having 2 to 4 sulfur atoms, such diphenyl polysulfide, dibenzyl polysulfide, dibenzoyl polysulfide, dibenzothiazoyl polysulfide, dithiobenzoyl polysulfide and a tetraalkylthiuram sulfide.
U.S. Pat. No. 5,816,944 discloses a solid golf ball having a core and cover covering the core, where the core is composed of a vulcanized molded material including a base rubber, a metal salt of α,β-unsaturated carboxylic acid, an organic peroxide, an organosulfur and/or metal-containing organosulfur compound, and a filler. The organic compound includes diphenyl disulfide, dixylyl disulfide, pentachlorothiophenol, thiobenzoic acid, morpholine disulfide, as well as zinc salts of thiophenols and thiocarboxylic acids.
U.S. Pat. No. 5,605,968 discloses a solid golf ball having a core and cover, where the core is made of a rubber composition including a base rubber, a metal salt of an unsaturated carboxylic acid, and a peroxide. In a preferred embodiment, pentachlorothiophenol or a metal salt thereof is added to the composition.
U.S. Pat. No. 5,252,652 discloses a solid golf ball where the golf ball core is formed from a rubber composition having a base rubber, an unsaturated carboxylic acid metal salt and an organic sulfur compound and/or a metal salt thereof. The organic sulfur compounds include thiophenols, such as pentachlorothiophenol, 4-butyl-o-thiocresol, 4-t-butyl-p-thiocresol, and 2-benzamideothiophenol; and sulfides, such as dixylyl disulfide, di(o-benzamidophenyl)disulfide and alkylated phenol sulfides. The metal-containing organic sulfur compounds include zinc salts of the above thiophenols and thiocarboxylic acids.
U.S. Pat. No. 5,697,856 discloses a solid golf ball having a core and cover, where the core includes a vulcanizing agent, a filler, an organic peroxide, and an organosulfur compound. The organosulfur compound can be diphenyl disulfide, dixylyl disulfide, ditolyl disulfide.
U.S. Pat. Nos. 6,468,168 discloses a golf ball having a solid core that may be formed from the use of sulfur bearing accelerators for rubber vulcanization, such as benzothiazyl disulfide and 2-mercaptobenzothiazole.
However, it is desirable to have golf ball compositions that use lower amounts of crosslinker, such as monoacrylate, diacrylate, triacrylate and their metallic derivatives, particularly for lower cost formulations or in formulations where lower levels of crosslinkers are preferred, without compromising golf ball playability. The compositions of the present invention provided golf balls with increased compression without the use of additional crosslinkers, such as zinc diacrylate.